Inductive Rotational Sensing with EMI Immunity
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Solution Overview
Problem
Rotational sensing systems for motors are susceptible to electromagnetic interference (EMI) from the stator magnetic field, which affects the accuracy of sensing motor rotation information such as frequency, angle, and direction.
Innovation Solution
A rotational sensing system using an inductive sensor with a rotating axial target surface and multiple conductive target segments, where the sensor generates a time-varying magnetic field to induce eddy currents, and the sensor response is converted into data representing rotational information, with paired sense coils and IQ phase offset configurations to reduce EMI and determine direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional rotational sensing systems are used for motor applications, then motor rotation information can be sensed, but the sensing accuracy deteriorates due to electromagnetic interference from the stator magnetic field
Solution Approach 1:
The patent extracts the sensing function from the motor control system by using a separate inductive sensor that independently measures rotor position and speed. This separation removes the sensing system from the harmful electromagnetic environment of the motor controller, eliminating EMI susceptibility while maintaining accurate rotational measurement capability
Solution Approach 2:
The patent introduces an inductive sensor as an intermediary measurement device that uses magnetic field coupling through the rotor structure to obtain rotational information without direct electrical connection to the motor control circuitry. This intermediary approach allows accurate sensing while isolating the measurement system from electromagnetic interference
2Object-affected harmful factors
If inductive sensing with rotating axial target surface is implemented, then susceptibility to common mode EMI is reduced, but device complexity increases due to multiple sense coils and target segments
Solution Approach 1:
The patent segments the sensing function into multiple sense coils arranged around the rotor circumference, each monitoring a specific angular position. This segmentation enables the system to reconstruct complete rotational information from distributed measurements while maintaining immunity to common mode EMI through differential measurement techniques
Solution Approach 2:
The patent combines multiple sense coil measurements into a unified rotational position and speed calculation. By merging the output signals from distributed sense coils and processing them through coordinate transformation algorithms, the system achieves accurate rotational sensing with enhanced EMI rejection capability
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system effectively senses motor rotation with reduced susceptibility to common mode EMI, providing accurate rotational frequency, angle, and direction information, and enhances sensitivity and resolution through sinusoidal sensor responses.
Implementation Method 1
driving excitation current to the sense coil to project a time-varying magnetic sensing field (B-field) toward the axial target surface, thereby inducing eddy currents in the target segment as it rotates under the sense coil
Implementation Method 2
inducing eddy currents in the target segment as it rotates under the sense coil
Data Source
AI summary
A rotational sensing system is adaptable to sensing motor rotation based on eddy current sensing. An axial target surface is incorporated with the motor rotor, and includes one or more conductive target segment(s). An inductive sensor is mounted adjacent the axial target surface, and includes one or more inductive sense coil(s), such that rotor rotation rotates the target segment(s) laterally under the sense coil(s). An inductance-to-digital converter (IDC) drives sensor excitation current to project a magnetic sensing field toward the rotating axial target surface. Sensor response is characterized by successive sensor phase cycles that cycle between LMIN in which a sense coil is aligned with a target segment, and LMAX in which the sense coil is misaligned. The number of sensor phase cycles in a rotor rotation cycle corresponds to the number of target segments. The IDC converts sensor response measurements from successive sensor phase cycles into rotational data.